The volcanic evolution of Syrtis Major Planum, Mars

Abstract

This thesis explores the geological history of the Syrtis Major Planum volcanic province on Mars. The primary aims are (i) to differentiate the various units that make up the lava plain of Syrtis Major Planum, (ii) to investigate the formation of the central caldera complex, and (iii) to understand how the volcanic architecture has evolved over time in the regional contex. The methodology applied is that of planetary geological mapping using remote sensing data. Two new morpho-stratigraphic maps of Syrtis Major Planum have been produced. Map 1, a 1:2,000,000 scale map, uses 100 m/pixel THEMIS data as the base layer, and draws on 6 m/pixel CTX data to provide additional information. Map 2 is a 1:250,000 scale map of the Nili Patera caldera and uses base layer mosaics of CTX data and CTX Digital Terrain Models. The mapping shows that there were two major phases of magmatism at Syrtis Major. The first phase (~3.6 Ga A¢â‚¬â€œ ~3.2 Ga) consisted of tube-fed lava plains interleaved with giant (>300 km) tabular lava flows emplaced from the centre of the planum. By the end of this phase, a fractionally crystallised magma reservoir, partially melting the hydrated sediments of the underlying Noachian highlands, had developed. The eruptive products of this magma reservoir include an ignimbrite, now exposed in Nili Patera. The second phase of magmatism (~2.7 Ga - ~2.2 Ga) consisted of temporally sporadic volcanism, spatially concentrated in the central caldera complex, and includes two examples of high-silica lava units. These derived from partial melting of the fractionally crystallised magma reservoir in the presence of hydrothermal fluids. The evolution of lava emplacement style and composition over time is best explained by the interaction between the waxing to waning stages of a mantle plume with the underlying Noachian terrain. This interaction led to the distinctive morphology of the volcanic shield, the explosive formation of the calderas, and the unusual compositions found within the central caldera complex. The volcanism of Syrtis Major is therefore defined both by the epoch in which it occurred, and the composition of the crust in which it formed.